The present invention relates to a method of and arrangement for treatment and disinfection of swimming and bathing reservoir water with the use of chlorine and ozone and deals particularly with ozonization of natural water.
The treatment of swimming and bathing reservoir water, which will be referred to herein below shortly as bathing water, has the object of guaranteeing at any time in the reservoir a water quality which excludes an infection risk for the bathers. For this purpose not only sufficiently high disinfection action must be maintained in the bathing water, but also it is important that the water outside of the reservoir is continuously freed from dissolved and undissolved impurities and microorganisms contained in the bathing water. For providing this water treatment outside of the reservoir, the reservoir water is continuously circulated, the withdrawn natural water is purified, disinfected, and supplied back into the reservoir with addition of a surplus of a disinfection medium as pure water. The relations here are very complex since the "swimming bath" system is influenced by a plurality of parameters which will not and cannot be discussed in their entirety. This problem is discussed in several publications, for example "KOK-Richtlinien fuer den Baderbau", 2. Auflage (1982), W. Tummels Verlag, Nurnberg; W. Roeske, "Schwimmbeckenwasser", Anforderungen-Aufbereitung-Untersuchung, Verlag O. Haase, Lubeck (1980); and especially in"Deutsche Norm DIN 19 643 Aufbereitung und Desinfektion von Schwimm- und Badebeckenwasser", April 1984, developed from Normenausschuss Wasserwesen in DIN Deutsches Institut fur Normung, in which a full list of further literature is presented.
A partial review of the requirements in accordance with DIN 19643 as to the water condition of the bathing water and to conventional steps for obtaining the desired quality of the reservoir or bathing water is presented later in Table 1.
As mentioned the disinfection is of special importance for the treatment of swimming reservoir water. A good disinfection agent must rapidly destroy or deactivate pathogenic germs in water and maintain the number of germs as low as possible. The bathing water must have a colony number of at most 100 per ml and Escheria coli bacteria (E. coli) as indicator germs for fecal impurities must not be detectable. In the ideal case the disinfection agent must be algicidal, fungicidal, bactericidal and virus deactivating, or in other words have a wide action spectrum. It should be taken into consideration (as disclosed in the publication Roeske, mentioned herein above, pages 204 et seq.) that the action of the disinfection agent must not only provide a direct chemical influence upon the microorganisms, but must also produce and maintain a redox potential in water, at which the microorganisms cannot survive. A certain redox system with a limited redox potential range and a certain pH value is present in the cell of a microorganism. When the redox potential of the surrounding water exceeds a limiting value of this range, it affects the metabolism of the microorganism, making it incapable of maintaining life. A "safety" redox potential for swimming bath water has a value of above approximately 600 mV for killing after an operating time of below one minute.
The disinfection agent must be used in a minimum concentration, so that it does not corrode the mechanical devices and does not have toxic or damaging side effects upon the bathers. It must be taste and odor-neutral, sufficiently stable in water for producing a sufficient and prolonged germ destroying action (depot action), must provide in addition to the disinfection action also an oxidizing action upon the materials contained in the water without producing damaging compounds with it, must not additionally load the water in that the reaction products must biologically decompose, must be produced with economically acceptable costs, and moreover must allow reliable, safe and accurate dosing and be reliable, simple and fast for determination of its concentration in water. Such an ideal disinfection agent is not known, while chlorine gas and some chlorine compounds satisfy a great part of the enumerated requirements. For bathing water disinfection, especially chlorine gas is a good choice as a disinfection agent. The disadvantages which are connected with the use of chlorine are well known, and in addition to odorous annoyance, it leads to eye irritation and skin incompatibility. As for the odorous annoyance and eye irritation it has been recognized that only the elementary chlorine dissolved in water or its hydrolysis products such as hydrochloric acid or hydrochlorous acid are responsible, but also the conversion products of ammonia derivatives (chloroamines) which are present in water are responsible for this phenomenon. In the chloroamines the chlorine is present as "bound" chlorine which however can be partially released.
For bathing water treatment, also ozone found its use. It is a strong oxidation and disinfection agent which can be used for water treatment. Ozone has very good bactericidal, virucidal and sporocidal properties and can partially flocculate colloidal materials distributed in water. Furthermore, it improves the odor, the taste and the optical properties of the water. The oxidizing decomposition of organic water loading materials is increased by ozone. The disadvantages of the ozone is that it is very poorly soluble in water, is destroyed relatively fast, and because of its considerable toxicity must not be used in reservoir water. This leads to the fact that the ozone cannot be utilized as depot oxidant and disinfecter in reservoir water, however is used with high cleaning advantages during water treatment outside the bathing reservoir. As compared with the use of a pure chlorine for water treatment, the ozone when used in combination of chlorine and ozone allows saving of considerable quantities of chlorine. It has been known in the prior art to provide such conditions that the natural water withdrawn from the reservoir after at least one filtration is treated with ozone in surplus for destroying or inactivating the microorganisms contained in natural water and decomposing the organic loading material, and after the ozonization the chlorination of natural water takes place which is supplied into the reservoir. Because of the toxicity of the ozone, conventionally the water after the ozonization and before the chlorination is supplied through an activated carbon filter, in which the ozone dissolved in water is catalytically decomposed. In accordance with the KOK regulations the pure water which flows to the reservoir must have no ozone or an ozone content which does not exceed 0.01 g ozone/m.sup.3 fresh water.
The production of ozone and the ozonization of the natural water (occasionally identified herein below as treatment water if the not yet pure natural water has been subjected to at least one purifying step) is performed approximately in the following manner. Ozone is produced mainly from air, in some cases also from oxygen, and as a rule by quiet electrical discharge with voltage between 6000 and 20,000 V. In the case of air, ozone-air mixtures with an ozone gas concentration of approximately 2 volume percent is produced. For production of lg of ozone with the use of dry atmospheric air, an energy consumption of 15-30 Wh is required. In the above described circumstances the initial gas such as air or oxygen gas must contain neither moisture, nor dust or catalytically active substances, to prevent a premature destruction of the formed ozone. The utilized oxygencontaining gas must be mechanically purified as far as possible and dried to a dew point under 228 K (-45.degree. C.).
A modern ozone producing installation with a throughput of approximately 800-1000 g of ozone per hour costs, with required auxiliary units and devices, approximately 500,000 DM or more. It is a high technology installation with maintenance expenses which are not insignificant, and it requires skilled maintenance personnel. As for the operating costs, the energy cost with an energy consumption of 15-30 kWh per 1 kg ozone is a great portion thereof. For an ozone consumption of for example 1.15 kg/h which is suitable for an indoor pool identified as the bath number 3 in Table 2, the energy consumption for the ozonization amounts to approximately 1714 -35 kWh per hour or approximately 20014 -400 kWh per day for 12-hour operation. For outdoor pools, particularly outdoor pools with wave operation, the ozone consumption and its costs are even higher.
The produced ozone is supplied into the treatment water through injectors or in scrubbers which operate in accordance with the counter-current principle. In the prior art 0.5-1.5 g of ozone is consumed for each m.sup.3 of water. This ozone addition is very high to provide very good disinfection and oxidation effect of the ozone and is explained by the low solubility of the ozone in water and the technique of its use. In accordance with this technique the ozone in counterflow containers or in reaction hoses is bubbled in form of more or less big gas bubbles of the air-ozone mixture (mixing ratio ozone: air approximately 1:50) under normal pressure through the water, or in the case of reaction hoses with conventional vertical winding course mixes poorly with the aqueous phase and only flows more or less along it. The reaction times of the ozones with the water or in other words the average dwelling time of the water in the reaction containers, also amounts to between 1 and 1.5 minutes.
All known ozonization methods operate in the open for the ozone-air mixture. The considerable gas quantities which have not dissolved in water are withdrawn from the reaction vessel through its head, and because of the physiological requirements of an ozone-free reservoir water, the ozonized treatment water must be finally cleaned from ozone. In general, this ozonization technique is very expensive both in view of its investment costs and its operating costs, and the economy of the disinfection agent chlorine outweighs the ozonization costs only by a small fraction. The special advantage of the ozonization lies however in a direct effect of the reduced chlorine utilization. In the event of the ozone assisted bathing water treatment, the chlorine as opposed to the pure chlorine utilization, no longer plays the double role of the cleaning of the natural water and the adjustment and maintenance of the chlorine level of "free chlorine" in the reservoir water, but it performs only the last mentioned function. As a result of this, there is a lower concentration in the reservoir water of reaction products of chlorine in particular the undesirable chloroamines, and in general a better water quality is obtained, so that the circulation intervals for the reservoir water can be reduced.
Because of the installations and cost required for the conventional ozonization technique, the water treatment with chlorine and ozone has not found a general application. Countries with hundreds and thousands of bathing facilities are known, in which a chlorine-ozone treatment is not used at all. Moreover, a conversion from swimming baths which operate purely with chlorine to a chlorine-ozone treatment of the bathing water has never been realized in the prior art.
The invention is based on these circumstances.